I have a website with all handy tools, for example, Random Word Generator, Separate a list, etc. Now I want to boost my SEO and one of the things I want to add is Schema.org markup. So I've taken a look at the Schema.org Full Hierarchy and what should I use? Tool? Instrument? HowToTool? Here is the html5 code for one of my pages and a screenshot.
I recommend using https://schema.org/SoftwareApplication. You must add a price though (i.e. "free" if no price), otherwise, you will annoy Google. Personally, I would take the example that Google gives here: google as a template and fill in with your own info. Always check Googles "Guidelines" for what is "required". Then test it here: Google testing tool